Imaging apparatus and control method therefor

ABSTRACT

An imaging apparatus includes an imaging unit configured to perform photoelectric conversion of an optical image, an optical zoom unit configured to perform optical magnification variation in response to a zooming operation, an electronic zoom unit configured to perform electronic magnification variation on a signal output from the imaging unit, and a controller configured to operate the electronic zoom unit together with the optical zoom unit in a first zoom range in response to the zooming operation, to operate the optical zoom unit without operating the electronic zoom unit in response to the zooming operation in a second zoom range, which is closer to a telephoto side than the first zoom range, and to operate the electronic zoom unit together with the optical zoom unit in response to the zooming operation in a third zoom range, which is closer to the telephoto side than the second zoom range.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of U.S. application Ser. No.12/341,921, filed Dec. 22, 2008, which claims priority to JapanesePatent Application No. 2007-336843 filed Dec. 27, 2007, which are herebyincorporated by reference herein in their entireties.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a technique for controlling opticalzooming and electronic zooming of an imaging apparatus.

2. Description of the Related Art

Video cameras and digital cameras serving as imaging apparatuses aredemanded to mount a high magnification zooming function to enabletelephotography. To this end, various attempts have been made to achievethe high magnification zoom function by improving the performance of anoptical zoom lens. However, generally, as the magnification of theoptical zoom lens is increased, a lens system is increased in size andweight . In addition, the increase in size and weight tends to result inan increase in cost thereof. Thus, a method has been proposed, whichachieves a high magnification by combining optical zoom for opticallyperforming enlargement/reduction of an object image utilizing opticalperformance of a lens with electronic zoom for electronically performingenlargement/reduction of an image signal output from an image sensor.

For example, Japanese Patent Application Laid-Open No. 2000-184259discusses the following method. That is, at a wide-angle end side, azooming up operation is performed by increasing the magnification ratioof electronic zoom. When the magnification ratio reaches a certainvalue, optical zoom is started to move to a telephoto side to furtherperform a zooming up operation.

However, generally, in a case where images having the same number ofpixels are generated, better image quality of the images is obtained byusing more pixel-lines (hereunder sometimes referred to simply as lines)output from an image sensor. In view of this fact, technical ideasdiscussed in Japanese Patent Application Laid-Open No. 2000-184259 causethe following problem. That is, in a case where the optical zooming isused to perform zooming up, the number of lines to be extracted from thelines output from the image sensor satisfies the number of linesdisplayed in a monitor. However, then, the number of lines to beextracted therefrom becomes smaller. Therefore, the image quality of theimage is degraded. This is because a zooming up operation is performedby increasing the magnification ratio of electronic zoomingpreferentially than the optical zooming up operation.

SUMMARY OF THE INVENTION

The present invention is directed to an imaging apparatus capable ofrealizing a higher magnification zooming operation using a combinationof optical zooming and electronic zooming, and further capable ofpreventing degradation of image quality.

According to an aspect of the present invention, an imaging apparatusincludes an imaging unit configured to perform photoelectric conversionof an optical image, an optical zoom unit configured to perform opticalmagnification variation in response to a zooming operation, anelectronic zoom unit configured to perform electronic magnificationvariation on a signal output from the imaging unit, and a controllerconfigured to operate the electronic zoom unit together with the opticalzoom unit in a first zoom range in response to the zooming operation, tooperate the optical zoom unit without operating the electronic zoom unitin response to the zooming operation in a second zoom range, which iscloser to a telephoto side than the first zoom range, and to operate theelectronic zoom unit together with the optical zoom unit in response tothe zooming operation in a third zoom range, which is closer to thetelephoto side than the second zoom range.

Further features and aspects of the present invention will becomeapparent from the following detailed description of exemplaryembodiments with reference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate exemplary embodiments, features,and aspects of the invention and, together with the description, serveto explain the principles of the invention.

FIG. 1 is a block diagram illustrating a configuration of an imagingapparatus according to an exemplary embodiment of the present invention.

FIG. 2 is a diagram illustrating an operation of the imaging apparatusaccording to the exemplary embodiment of the present invention.

FIG. 3 is a flowchart illustrating the operation of the imagingapparatus according to the exemplary embodiment of the presentinvention.

FIG. 4 is a diagram illustrating an operation of extracting a number oflines from an image stored in a memory of the imaging apparatusaccording to the exemplary embodiment of the present invention.

FIG. 5 is a diagram illustrating an operation of extracting anothernumber of lines from the image stored in the memory of the imagingapparatus according to the exemplary embodiment of the presentinvention.

FIG. 6 is a diagram illustrating an operation of extracting stillanother number of lines from the image stored in the memory of theimaging apparatus according to the exemplary embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Various exemplary embodiments, features, and aspects of the inventionwill be described in detail below with reference to the drawings.

In the following description, the term “optical zoom” means “tooptically enlarge or reduce an object image utilizing the opticalperformance of a lens”. Further, the term “electronic zoom” means “toenlarge or reduce an image by electronically enlarging or reducing animage signal that is output from an image sensor”.

FIG. 1 is a block diagram illustrating an imaging apparatus according toan exemplary embodiment of the present invention. The imaging apparatusincludes an optical zoom lens 1, an image sensor 2, a video signalprocessing circuit 3, a reduction processing circuit 4, and asynchronous dynamic random access memory (SDRAM) 5. The optical zoomlens serves as an imaging lens. The image sensor 2 (charge-coupleddevice (CCD) or a complementary metal-oxide semiconductor(CMOS))converts (i.e., performs photoelectric conversion) an opticalimage, formed by the optical zoom lens 1, into an electric signal. Thevideo signal processing circuit 3 performs video signal processing suchthat a signal output from the image sensor 2 conforms to a predeterminedvideo standard. The reduction processing circuit 4 electronicallyperforms reduction processing on the video signal. The synchronousdynamic random access memory (SDRAM) 5 temporarily saves video signaldata when reduction processing is performed on a video signal. Theimaging apparatus further includes a monitor output circuit 6 foroutputting a video signal through an output terminal (not shown) to amonitor, a recording image output circuit 10 for outputting a videosignal to be recorded on a recording medium, a timing generation (TG)control circuit 9 for generating horizontal and vertical driving signalsfor the image sensor 2, a microcomputer 7 serving as a control unit forcontrolling the entire system, and an optical zoom control circuit 8 forcontrolling a optical magnification variation operation (hereunderreferred to also as optical zoom) using the optical zoom lens 1.

Hereinafter, an operation of changing an electronic zoom magnificationaccording to an optical zoom magnification, in an imaging apparatusconstructed as described above, is described.

An object image formed by the optical zoom lens 1 is converted into anelectric signal by the image sensor 2. Then, the electric signal isinput to the video signal processing circuit 3. In the video signalprocessing circuit 3, white balance processing for converting raw colorinto color close to memory color is performed on the electric signal.The video signal processing circuit 3 performs non-linear signalprocessing, such as gamma correction, or aperture correction processingfor adding a perceived resolution. Then, the video signal processingcircuit 3 outputs a video signal to the reduction processing circuit 4.

The TG control circuit 9 is configured to read data of, e.g., 2048 linesarranged in the vertical direction so as to read all effective pixels ofthe image sensor 2. Then, the reduction processing circuit 4 performsdata extraction from the memory (hereunder sometimes referred to simplyas memory-data extraction) to extract data of 480 lines from the data of2048 lines as video signals so that the extracted data of 480 lines canbe output as video signals. Subsequently, the reduction processingcircuit 4 performs reduction processing on the extracted data of 480lines. Then, the reduction processing circuit 4 outputs to the monitoroutput circuit 6 a digital video signal that has undergone the reductionprocessing. Subsequently, the monitor output circuit 6 converts thedigital video signal into an analog signal and outputs it.

When zoom processing is performed in response to a photographer'szooming operation to zoom up an image signal output from the monitoroutput circuit 6, the microcomputer 7 outputs to the optical zoomcontrol circuit 8 a control signal, which drives the optical zoom lens 1toward the telephoto end. Concurrently with this, according to a zoomposition of the optical zoom lens 1, the microcomputer 7 determines anextraction range. Then, the microcomputer 7 instructs a reduction ratioto the reduction processing circuit 4.

FIG. 4 illustrates a case, more specifically and schematically, wherememory-data extraction is performed, in which video signals of 1920lines are extracted from video signals of 2048 lines of all effectivepixels of the image sensor 2. As is seen from FIG. 4, substantially allof the effective pixels of the image sensor 2 are extracted. Therefore,a wide-angle side imaging is performed.

Next, FIG. 5 schematically illustrates a case where memory-dataextraction is performed, in which video signals of 960 lines areextracted from the video signals of 2048 lines of all effective pixelsof the image sensor 2. As is seen from comparison between FIGS. 4 and 5,video signals illustrated in FIG. 5 are extracted from an inner range of2048 lines of all effective pixels of the image sensor 2.

Reasons, for which the number of lines to be extracted is set at 960,are described below. The number of such lines, i.e., 960, is an integralmultiple of the number of lines, i.e., 480, of one frame image to beoutput to a monitor or to be recorded on a recording medium. That is,reduction processing is performed at a reduction ratio of 1/2 on animage having 960 lines to generate an image having 480 lines. At thisreduction ratio, when one frame image having 480 lines is generated, as960 is dividable by 480, interpolation processing between lines is notnecessary. Thus, when a value of 960 is employed as the number of lines,the degradation of image quality is small. Consequently, the number oflines to be extracted is set to be 960. Accordingly, the number of linesto be extracted is set to be nX (n is an integer), because the value ofnX is divisible by the number X of lines of a frame image to be recordedor displayed.

In addition, as memory-data extraction is performed by extracting videosignals of 960 lines from those of 2048 lines, the remaining area of theimage can be effectively used. More specifically, the remaining area canbe used for electronic image stabilization, which reduces influence ofimage vibration due to camera shake or the like on a monitor outputimage and a recording image. On the other hand, when video signals of1920 lines are extracted, as described above referring to FIG. 4, aregion of effective pixels to be available for electronic imagestabilization is smaller than the region when video signals of 960 linesare extracted. However, when video signals of 1920 lines are extracted,an imaging can be performed at a wider angle than at an angle when videosignals of 960 lines are extracted. An influence of camera shake on animage captured at a wide-angle side is smaller than the influence of thecamera shake on an image captured at a telephoto side. Accordingly, at awide-angle side, a region of effective pixels, which is used forelectronic image stabilization, can be reduced, as compared with theregion used at a telephoto side.

FIG. 6 is a diagram schematically illustrating memory-data extractionfor extracting video signals of 480 lines from those of all 2048 linesof effective pixels of the image sensor 2. As is seen from FIG. 6, videosignals are extracted from a further inner range, than the rangeillustrated in FIG. 5, of all 2048 lines of effective pixels of theimage sensor 2. The number of lines to be extracted is set at 480,because the number of lines to be output to a monitor and to be recordedon a recording medium is 480. In this case, interpolation processing onan image is not necessary, and thus, the degradation of image quality issmall.

In addition, as described above, at a telephoto side, a region ofeffective pixels, which is available for electronic image stabilization,can be increased as compared with the region at a wide-angle side.

The electronic zoom for performing electronic magnification variation isperformed in the above-described manner.

FIG. 2 illustrates an operation of the imaging apparatus according tothe exemplary embodiment of the present invention. The right-sideordinate axis represents an optical zoom magnification. The optical zoommagnification indicated in FIG. 2 ranges from 1× to 20×. The left-sideordinate axis represents the number of lines to be extracted from thememory. The number of lines to be extracted from the memory ranges from480 to 1920. The “number of lines to be extracted from the memory”determines the number of lines from which 480 lines are generated whensignals of 2048 lines are input from the image sensor 2 to the signalprocessing circuit 3 to generate video signals of 480 lines. The maximumnumber of lines to be extracted from the memory is 1920, while theminimum number of lines to be extracted from the memory is 480. Thus,the magnification of the electronic zoom is 4×. Incidentally, the numberof 480 corresponds to the number of lines included in one frame image tobe output to a monitor or to be recorded on a recording medium.

In FIG. 2, the abscissa axis represents a total zoom magnificationobtained by multiplying the optical zoom magnification by the electroniczoom magnification. More specifically, a maximum total zoommagnification of 80× is obtained by multiplying an optical zoommagnification of 20× by an electronic zoom magnification of 4×. In FIG.2, a dashed line represents a process of changing the optical zoommagnification. A solid line represents a process of changing the numberof lines to be extracted from the memory (the electronic zoommagnification is assumed to be 1× when the number of lines to beextracted from the memory is 1920).

Next, the process of changing the zoom magnification, which iscontrolled by the microcomputer 7, is described hereinafter referring toFIG. 2. For simplicity of description, only the process of changing thezoom magnification from a wide-angle side to a telephoto side inresponse to a photographer's zooming operation is described below.However, the process of changing the zoom magnification from thetelephoto side to the wide-angle side can be performed similarly.

First, in a zoom range I, the optical zoom magnification is graduallyincreased from point A corresponding to the wide-angle end to point B atthe telephoto side. Concurrently with this, the number of lines to beextracted from the memory is gradually reduced from point Ecorresponding to 1920 lines. Thus, in the zoom range I, an optical zoomunit and an electronic zoom unit are operated concurrently with eachother.

In a zoom range II, the number of lines to be extracted from the memoryis fixed at 960 while the optical zoom magnification is increased from apredetermined magnification corresponding to point B to anotherpredetermined magnification corresponding to point C. Thus, in the zoomrange II, only the optical zoom unit is operated without performing anoperation of the electronic zoom unit.

The reasons, for which the number of lines to be extracted is set to be960, have been described above. That is, because the number of lines tobe output to the monitor is 480, an image having 480 lines to be outputcan be obtained by reducing the number of lines (i.e., 960) of an image,which is an integral multiple of (twice in this case) the number oflines to be output to the monitor (i.e., 480), to half. When the numberof lines of an image to be output is reduced to just half, the signalprocessing circuit does not perform interpolation between lines. Thus,there is no degradation of image quality. In addition, a region ofeffective pixels, which is other than the 960 lines, is available forelectronic image stabilization.

In a zoom range III, the optical zoom magnification is graduallyincreased from an optical zoom magnification corresponding tomagnification point C to another optical zoom magnificationcorresponding to magnification point D at the telephoto side.Concurrently, the number of lines to be extracted from the memory isgradually reduced from 960 corresponding to magnification point G to 480corresponding to magnification point H. Accordingly, in the zoom rangeIII, the optical zoom unit and the electronic zoom unit are operatedconcurrently with each other.

Incidentally, reasons, for which the number of lines to be extracted isset at 480, are that the number of lines to be extracted is equal tothat of lines to be output to the monitor or to be recorded on arecording medium, so that no degradation of image quality occurs, and aregion of effective pixels, which is other than the 480 lines, isavailable for electronic image stabilization.

Note that the term “concurrently” means that an optical zoom operationand an electronic zoom operation are performed concurrently. Thatincludes a case when the optical zoom operation and the electronic zoomoperation are performed at a time and a case when they are performedalternately. Each case can occur depending on the load of themicrocomputer 7 and/or the load of the optical zoom control circuit 8when zooming is performed.

FIG. 3 is a flowchart illustrating an operation of the microcomputer 7.

In step S301, the microcomputer 7 reads a zoom position of the opticalzoom. In addition, the read zoom position is set to be ZM. In step S302,the microcomputer 7 determines whether the position ZM is locatedbetween points A and B (illustrated in FIG. 2). If the position ZM islocated between points A and B (YES in step S302), the processingproceeds to step S303, in which the microcomputer 7 sets the number oflines to be extracted from the memory, and sets also extractionpositions of the lines in the memory.

If the position ZM is not located between points A and B (NO in stepS302), then in step S304, the microcomputer 7 determines whether theposition ZM is located between points B and C. If the position ZM islocated between points B and C (YES in step S304), then in step S305,the microcomputer 7 sets the extraction position in the memory whilefixing the number of lines to be extracted from the memory. If theposition ZM is not located between points B and C (NO in step S304),then in step S306, the microcomputer 7 sets the number of lines to beextracted from the memory and the extraction position in the memoryaccording to the zoom position.

Incidentally, the extraction position in the memory is determined byconsidering the electronic image stabilization operation.

Thus, according to the present embodiment, in the zoom range I, theelectronic zoom unit is operated together with the optical zoom unit inresponse to a photographer's zooming operation. Further, in the zoomrange II, which is closer to the telephoto side than the zoom range I,the optical zoom unit is operated without operating the electronic zoomunit. Furthermore, in the zoom range III, which is closer to thetelephoto side than the zoom range II, the electronic zoom unit isoperated together with the optical zoom unit. Accordingly, wide-angleimaging can be performed at a wide-angle side of the zoom range usingthe effective pixel region of the image sensor 2 effectively. In anintermediate zoom range, the number of lines to be extracted from thememory at the electronic zooming is fixed. That is, the magnificationratio is fixed at a ratio at which good image quality is obtained.Further, in a zoom range at a telephoto side, the degradation of imagequality of an image to be output to the monitor or to be recorded on arecording medium can be reduced as much as possible.

According to the present embodiment, when the zooming up by the opticalzoom is performed, the number of lines to be extracted from lines outputfrom the image sensor satisfies the number of lines to be displayed onthe monitor. In addition, the degradation of the image quality due to asmall number of the extracted lines can be reduced. Accordingly,high-magnification zooming can be realized by using the optical zoomunit and the electronic zoom unit, while the degradation of imagequality can be reduced.

In the foregoing description, it has been described, as an example, thecase where the number of lines to be output to the monitor or to berecorded on a recording medium is 480. However, technical ideasaccording to the present invention can be applied to a case where thenumber of lines to be output to the monitor or to be recorded on arecording medium is 1080.

Further, although the electronic zoom has been described by focusing onthe number of lines to be extracted from the memory, signal processingin each line (extending in the horizontal direction), as viewed in FIGS.4 through 6, is similarly performed. The present embodiment can beapplied to the number of pixels corresponding to an output signal fromthe image sensor 2, the number of pixels to be output to the monitor, orthe number of pixels to be recorded on a recording medium.

Furthermore, in the foregoing description, the apparatus has beendescribed as a system in which the microcomputer 7 determines anextraction-data range of lines of pixels represented by signals outputfrom the image sensor 2 according to the zoom position of the opticalzoom lens 1. Regarding this respect, the apparatus can be modified suchthat the microcomputer 7 controls the zoom position of the optical zoomlens 1 in response to a photographer's zooming operation and determinesa range of lines to be extracted from lines of pixels output from theimage sensor 2 based on table data.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all modifications, equivalent structures, and functions.

1. An imaging apparatus comprising: an imaging unit configured toperform photoelectric conversion of an optical image; an optical zoomunit configured to perform optical magnification variation in responseto a zooming operation; an electronic zoom unit configured to performelectronic magnification variation on a signal output from the imagingunit; and a controller configured to operate the electronic zoom unittogether with the optical zoom unit in a first zoom range from awide-angle side in response to the zooming operation, to operate theoptical zoom unit without operating the electronic zoom unit in responseto the zooming operation in a second zoom range, which is closer to atelephoto side than the first zoom range, and to operate the electroniczoom unit together with the optical zoom unit in response to the zoomingoperation in a third zoom range, which is closer to the telephoto sidethan the second zoom range; wherein the first, second and third zoomranges constitute the total zoom range obtainable by the imagingapparatus in that the first zoom range extends from the wide-angle sideto a first point, the second zoom range extends from the first point toa second point, which is closer to the telephoto side than the firstpoint, and the third zoom range extends from the second point to thetelephoto side.
 2. The imaging apparatus according to claim 1, whereinthe controller operates the electronic zoom unit such that the number ofpixels corresponding to signals output from the imaging unit in thefirst zoom range is larger than at least one of the number of pixelsoutput to a monitor and the number of pixels to be recorded on arecording medium.
 3. The imaging apparatus according to claim 1, whereinthe controller operates the electronic zoom unit such that the number ofpixels corresponding to signals output from the imaging unit in thesecond zoom range is an integral multiple of at least one of the numberof pixels output to a monitor and the number of pixels to be recorded ona recording medium.
 4. A method for controlling an imaging apparatusincluding an imaging unit configured to perform photoelectric conversionof an optical image, an optical zoom unit configured to perform opticalmagnification variation in response to a zooming operation, and anelectronic zoom unit configured to perform electronic magnificationvariation on a signal output from the imaging unit, the methodcomprising: operating the electronic zoom unit together with the opticalzoom unit in a first zoom range from a wide-angle side in response tothe zooming operation; operating the optical zoom unit without operatingthe electronic zoom unit in response to the zooming operation in asecond zoom range, which is closer to a telephoto side than the firstzoom range; and operating the electronic zoom unit together with theoptical zoom unit in response to the zooming operation in a third zoomrange, which is closer to the telephoto side than the second zoom range;wherein the first, second and third zoom ranges constitute the totalzoom range obtainable by the imaging apparatus in that the first zoomrange extends from the wide-angle side to a first point, the second zoomrange extends from the first point to a second point, which is closer tothe telephoto side than the first point, and the third zoom rangeextends from the second point to the telephoto side.